CancelMoose

CancelMoose (actually, these days, a program called AutoMoose) doesn't send cancel messages to the Usenet. Instead, it sends "notices" to alt.nocem.misc. These notices (that can also be generated by spam warriors) will then be read by NoCeM or similiar program that will hide the offending articles from the user.

[Usenet] The archetype and model of
all good spam-fighters. Once upon a time, the 'Moose would send
out spam-cancels and then post notice anonymously to
news.admin.policy, news.admin.misc, and
alt.current-events.net-abuse. The 'Moose stepped to the fore on
its own initiative, at a time (mid-1994) when spam-cancels were
irregular and disorganized, and behaved altogether admirably -
fair, even-handed, and quick to respond to comments and criticism,
all without self-aggrandizement or martyrdom. Cancelmoose[tm]
quickly gained near-unanimous support from the readership of all
three above-mentioned groups.

Nobody knows who Cancelmoose[tm] really is, and there aren't even
any good rumors. However, the 'Moose now has an e-mail address
(moose@cm.org) and a web site (http://www.cm.org.)

By early 1995, others had stepped into the spam-cancel business,
and appeared to be comporting themselves well, after the 'Moose's
manner. The 'Moose has now gotten out of the business, and is more
interested in ending spam (and cancels) entirely.